[Mesa-dev] [PATCH 4/4] glsl: Generated masked write instead of vector array index for UBO lowering

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

When reading a column from a row-major matrix, we would slot the single
value read into the vector using an ir_dereference_array of the vector
with a constant index.  This will (eventually) get optimized to a
masked-write, so just generate the masked write in the first place.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: Eric Anholt <eric at anholt.net>
---
 src/glsl/lower_ubo_reference.cpp | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/src/glsl/lower_ubo_reference.cpp b/src/glsl/lower_ubo_reference.cpp
index 026197d..9e5e951 100644
--- a/src/glsl/lower_ubo_reference.cpp
+++ b/src/glsl/lower_ubo_reference.cpp
@@ -357,17 +357,14 @@ lower_ubo_reference_visitor::emit_ubo_loads(ir_dereference *deref,
 
       for (unsigned i = 0; i < deref->type->vector_elements; i++) {
 	 ir_rvalue *chan = new(mem_ctx) ir_constant((int)i);
-	 ir_dereference *deref_chan =
-	    new(mem_ctx) ir_dereference_array(deref->clone(mem_ctx, NULL),
-					      chan);
-
 	 ir_rvalue *chan_offset =
 	    add(base_offset,
 		new(mem_ctx) ir_constant(deref_offset + i * matrix_stride));
 
-	 base_ir->insert_before(assign(deref_chan,
+	 base_ir->insert_before(assign(deref->clone(mem_ctx, NULL),
 				       ubo_load(glsl_type::float_type,
-						chan_offset)));
+						chan_offset),
+				       (1U << i)));
       }
    }
 }
-- 
1.8.1.4